1. Field of the Invention
The present invention relates to a through hole forming method for forming a though hole in a conductor laminated plate having a laminated structure of a conductor layer and an insulating layer, and a printed circuit board manufacturing method including the through hole forming method.
2. Description of the Background Art
Conventionally, printed circuit boards have been used for various types of electric equipment or electronic equipment. The printed circuit boards generally have laminated structures of insulating layers composed of polyamide and conductor layers composed of a copper foil, for example, formed on both surfaces of the insulating layers. The insulating layers and the conductor layers may, in some cases, be made to adhere to each other by adhesive layers. The conductor layers are subjected to etching, to have predetermined patterned conductors.
When such printed circuit boards are manufactured, a copper laminated plate having the above-mentioned laminated structure, for example, is used. The copper laminated plate is obtained by previously laminating a plurality of conductor layers composed of a copper foil or the like on an insulating layer composed of polyamide or the like using an adhesive layer.
The copper laminated plate is provided with a through hole for electrically connecting the plurality of conductor layers. The through hole is formed by irradiating laser light onto the copper laminated plate. After the through hole is thus formed, a metal thin film (an electroless plating layer and an electrolytic plating layer) for electrically connecting conductor layers are formed on a surface of the through hole (see JP 2005-072324 A, for example).
When the laser light is irradiated in order to form the through hole in the copper laminated plate, as described above, however, a surface of the adhesive layer on an inner wall of the through hole that is being formed is gouged with heat energy generated within the through hole, to have a concave (or convex) shape. As a result, the metal thin film is disconnected in forming the metal thin film, so that electrical connection reliability is degraded.